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BIG PHYSICS, BIG QUESTIONS –

Californian beach boasts world’s pickiest females

By Gaia Vince

US scientists believe they may have found the pickiest females in the world. And size does matter – when it comes to the creature’s abode – a new study suggests.

Californian fiddler crab females often check out more than 100 males – even inspecting the hapless side-crawlers’ bachelor pads – before selecting their mate, according to Catherine deRivera, at the University of California in San Diego, US. “Most animals sample just a few mates, presumably because search costs override the benefits of lengthy searches,” she says.

During seduction, the male fiddler crab stands at the entrance of his waterfront burrow and with a “come hither” wave beckons the female over. Interested females eye up the males and if they like what they see, partially or fully enter their potential den of iniquity to size it up.

Once she has picked her male, the female crab enters his home and plugs the hole to his burrow. Once comfy, the crabs will mate and incubate their eggs, which later hatch to be flushed from the estuary by the tides.

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Reducing predation

But it seems that fiddler crab females are not being pointlessly demanding – the survival chances of their offspring appears to be strongly linked to the size of their mate and, more importantly, his corresponding abode.

“The size of the male’s burrow affects the development time of his larvae. A burrow of just the right size allows larvae to hatch at the safest time – at the peak outward night-time flow of the biweekly tidal cycle,” deRivera explains. “Overly-wide burrows speed incubation, so cause the larvae to hatch too early and miss the peak tides.”

Larvae are successfully released during the peak of the night tides “only when females incubated in burrows that allowed larvae to exit the estuary swiftly and thus reduce predation risks, but not when the females incubated in burrows that were too wide or too narrow”.

However, some female crabs are pickier than others, deRivera found, and larger females could not afford to be so picky. The larger female crabs took a lot less time choosing their mate and entered fewer burrows, primarily because many of the burrows were too small to accommodate them in the first place, preventing the successful incubation of their eggs.